1. Field of the Invention
This invention relates to a method of predicting a future deteriorated and damaged state of a structural member of a prime mover or the like used under a severe condition, e.g., a member of a gas turbine or a jet engine, on the basis of used conditions and the result of inspection of the structural member, and to a prediction apparatus for use with the method.
2. Description of the Related Art
Recently, environments in which structural members of gas turbines and jet engines are used have become severer, and deterioration and damage in such structural members, typically in gas turbines for generating electric power, have become noticeable. Gas turbines recently developed are used under severe conditions such that main component parts, such as moving blades, stationary blades and combustors, are exposed to combustion gas at a high temperature exceeding 1,000.degree. C., and the turbine is started and stopped frequently. Therefore, a deterioration due to a change with time and damage due to generation of cracks, voids, separation an the like in the structure of the materials of structural members of the gas turbines have become considerably large.
Conventionally, models for predicting a course of deterioration and damage in each of structural members of gas turbines have been proposed. For example, a conception of a cumulative damage law has been widely applied with respect to generation of cracks due to fatigue and creep.
An evaluation method based on the cumulative damage law is used as described below. As shown in FIG. 27, damage caused in a case where fatigue and creep have a complex effect is evaluated by performing temperature-stress analysis, using a material data bank, and correcting material characteristic data on the basis of an operation history and inspection. Creep damage .PHI.c and fatigue damage .PHI.f are calculated by the following equations: EQU .PHI.c=t/tr, .PHI.f=n/Nf (1)
where
t: operating time PA1 tr: creep rupture time PA1 n: startup times PA1 Nf: fatigue rupture times.
A creep-fatigue limit damage line shown in FIG. 27 is experimentally obtained from the combination of creep damage .PHI.c and fatigue damage .PHI.f at crack generation limits. This creep-fatigue limit damage line and the combination of creep damage .PHI.c and fatigue damage .PHI.f are compared to predict an accumulated state P1 and a future advanced state Pn of the damage.
Other methods in which the growth of a single macroscopic crack is predicted by destruction dynamics are now being used widely (which are, for example, a method proposed by Viswanathan in Damage Mechanics and Life Assessment of High-Temperature Components, ASM International, 1989, Chapter 1, pp 70-71, Chapter 6, p 301, Chapter 9 p 461, and a method described in Proceedings of International Conference on Life Assessment and Repair Technology or Combustion Turbine Hot Section Components, 1990, p 111).
The conventional methods are based on a conception that a deterioration and damage can be predicted if an initial state of a structural member is fixed and if a future operation prospect is determined. However, in a case where various kinds of deterioration and damage occur in a structural member under complex factors, the construction of a prediction model is very difficult and the advancement of deterioration and damage in the structural member is non-linear and depends largely upon the order of deterioration of potions of the structural member. Therefore, a small variation in an initial state may result in a large variation in the deteriorated and damaged state of the structural member. A multiplicity of thermal fatigue cracks can be observed in a stationary blade of a gas turbine as an example of damage to a structural member caused under complex factors. A phenomenon is known in which such thermal fatigue cracks grow complexly and synergistically, depending upon a temperature-stress distribution, a material structure distribution and interference between the cracks. A case where a deterioration and damage in a coating on a moving blades or the like of a gas turbine influence the advance of a deterioration and damage in a base member can be mentioned as an example of the problem relating to the order of deterioration and damage in a structural member. A method of predicting the advancement of damage under complex factors by simulation analysis (Nippon Gas Turbine Gakkai-shi, 19-76, 1992, p 78) has been proposed as a trial of damage prediction in such a case. However, deterioration and damage in structural members cannot always be predicted sufficiently by this method.
In the conventional methods for predicting a deterioration and damage in a structural member, it is difficult to construct a model of a deterioration and damage in the structural member if there are complex causes of the deterioration and damage or if the advancement of deterioration and damage is non-linear, and there is still a problem of how a prediction system is arranged to accurately predict the deteriorated and damaged state of a structural member in a case where the advancement of deterioration and damage cannot be correctly predicted.